Chemical device with thin conductive element

ABSTRACT

In one implementation, a chemical device is described. The sensor includes a chemically-sensitive field effect transistor including a floating gate structure having a plurality of floating gate conductors electrically coupled to one another. A conductive element overlies and is in communication with an uppermost floating gate conductor in the plurality of floating gate conductors. The conductive element is wider and thinner than the uppermost floating gate conductor. A dielectric material defines an opening extending to an upper surface of the conductive element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No. 61/868,942 filed Aug. 22, 2013 and 61/790,866 filed Mar. 15, 2013, the entire contents of which are incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

This disclosure, in general, relates to sensors for chemical analysis, and to methods for manufacturing such sensors.

BACKGROUND

A variety of types of chemical devices have been used in the detection of chemical processes. One type is a chemically-sensitive field effect transistor (chemFET). A chemFET includes a source and a drain separated by a channel region, and a chemically sensitive area coupled to the channel region. The operation of the chemFET is based on the modulation of channel conductance, caused by changes in charge at the sensitive area due to a chemical reaction occurring nearby. The modulation of the channel conductance changes the threshold voltage of the chemFET, which can be measured to detect and/or determine characteristics of the chemical reaction. The threshold voltage may, for example, be measured by applying appropriate bias voltages to the source and drain, and measuring a resulting current flowing through the chemFET. As another example, the threshold voltage may be measured by driving a known current through the chemFET, and measuring a resulting voltage at the source or drain.

An ion-sensitive field effect transistor (ISFET) is a type of chemFET that includes an ion-sensitive layer at the sensitive area. The presence of ions in an analyte solution alters the surface potential at the interface between the ion-sensitive layer and the analyte solution, due to the protonation or deprotonation of surface charge groups caused by the ions present in the analyte solution. The change in surface potential at the sensitive area of the ISFET affects the threshold voltage of the device, which can be measured to indicate the presence and/or concentration of ions within the solution. Arrays of ISFETs may be used for monitoring chemical reactions, such as DNA sequencing reactions, based on the detection of ions present, generated, or used during the reactions. See, for example, U.S. Pat. No. 7,948,015 to Rothberg et al., which is incorporated by reference herein in its entirety. More generally, large arrays of chemFETs or other types of chemical devices may be employed to detect and measure static and/or dynamic amounts or concentrations of a variety of analytes (e.g. hydrogen ions, other ions, compounds, etc.) in a variety of processes. The processes may, for example, be biological or chemical reactions, cell or tissue cultures or monitoring neural activity, nucleic acid sequencing, etc.

An issue that arises in the operation of large scale chemical device arrays is the susceptibility of the sensor output signals to noise. Specifically, the noise affects the accuracy of the downstream signal processing used to determine the characteristics of the chemical and/or biological process being detected by the sensors. It is therefore desirable to provide devices including low noise chemical devices, and methods for manufacturing such devices.

SUMMARY

In one exemplary embodiment, a chemical device is disclosed. The sensor includes a chemically-sensitive field effect transistor including a floating gate structure comprising a plurality of floating gate conductors electrically coupled to one another. A conductive element overlies and is in communication with an uppermost floating gate conductor in the plurality of floating gate conductors. The conductive element may be wider and thinner than the uppermost floating gate conductor. The sensor further includes a dielectric material defining an opening extending to an upper surface of the conductive element. Accordingly to an exemplary embodiment, the conductive element may comprise at least one of titanium, tantalum, titanium nitrite, and aluminum, and/or oxides and/or mixtures thereof. According to another embodiment, the distance between adjacent conductive elements in the chemical device is about 0.18 microns. In yet another embodiment, the thickness of the conductive element is about 0.1-0.2 microns. In one embodiment, the uppermost floating gate conductor in the plurality of floating gate conductors may have a thickness greater than a thickness of other floating gate conductors in the plurality of floating gate conductors. In another embodiment, the conductive element may comprise a material different from a material comprising the uppermost floating gate conductor. Accordingly to an exemplary embodiment, the conductive element may comprise a material different from a material comprising the uppermost floating gate conductor. According to another embodiment, an inner surface of the dielectric material and the upper surface of the conductive element define an outer surface of a reaction region for the chemical device. In yet another embodiment, the plurality of floating gate conductors is within layers that further include array lines and bus lines. In one embodiment, the chemical devices includes a sensor region containing the chemically-sensitive field effect transistor and a peripheral region containing peripheral circuitry to obtain a signal from the chemically-sensitive field effect transistor. In one embodiment, the conductive element is within a conductive layer that is only within the sensor region. In another embodiment, the conductive element comprises a material not within the peripheral region. Accordingly to an exemplary embodiment, the chemically-sensitive field effect transistor may include a floating gate structure comprising a plurality of conductors electrically coupled to one another and separated by dielectric layers, and the floating gate conductor may be an uppermost conductor in the plurality of conductors. According to another embodiment, a first layer of the dielectric material may be silicon nitride and a second layer may be at least one of silicon dioxide and tetraethyl orthosilicate, and the second layer defines sidewalls of the opening. In one embodiment, the chemical device may further comprise a microfluidic structure in fluid flow communication with the chemically-sensitive field effect transistor, and arranged to deliver analytes for sequencing.

In another exemplary embodiment, method for manufacturing a chemical device is disclosed. The method includes forming a chemically-sensitive field effect transistor including a floating gate structure comprising a plurality of floating gate conductors electrically coupled to one another. The method further includes forming a conductive element overlying and in communication with an uppermost floating gate conductor in the plurality of floating gate conductors. The conductive element is wider and thinner than the uppermost floating gate conductor. The method further includes forming a dielectric material defining an opening extending to an upper surface of the conductive element. Accordingly to an exemplary embodiment, the upper surface of the conductive element defines a bottom surface of a reaction region for the chemical sensor. According to another embodiment, an inner surface of the dielectric material and the upper surface of the conductive element define an outer boundary of a reaction region for the chemical sensor. In yet another embodiment, the conductive element is formed within a conductive layer that is only within a sensor region of the chemical device.

Particular aspects of one more implementations of the subject matter described in this specification are set forth in the drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of components of a system for nucleic acid sequencing according to an exemplary embodiment.

FIG. 2 illustrates a cross-sectional view of a portion of the integrated circuit device and flow cell according to an exemplary embodiment.

FIG. 3 illustrates cross-sectional of representative chemical devices and corresponding reaction regions according to an exemplary embodiment.

FIGS. 4 to 14 illustrate stages in a manufacturing process for forming an array of chemical devices and corresponding well structures according to an exemplary embodiment.

FIG. 15 illustrates a block diagram of an exemplary chemical device including an exemplary sensor region and an exemplary peripheral region, according to an exemplary embodiment.

DETAILED DESCRIPTION

Chemical devices are described that include low noise chemical devices, such as chemically-sensitive field effect transistors (chemFETs), for detecting chemical reactions within overlying, operationally associated reaction regions. A sensor of a chemical device may comprise a plurality of floating gate conductors with a sensing layer deposited on an uppermost floating conductor of the plurality of floating gate conductors. However, Applicants have found that adding an additional layer above uppermost floating conductor of the plurality of floating gate conductors that is dedicated to sensing has advantages that overcome the technical challenges and cost of the additional layer. For example, Applicants have found that advantages in the chemical devices described herein include providing enhanced lithographic process margin; (for example, prevent misalign of openings and/or burnout); and providing larger openings in the dielectric than would be possible were the sensing area directly on top of the uppermost floating gate conductor (for example, larger openings can accommodate more signal).

Exemplary chemical devices described herein have sensing surface areas which may comprise a dedicated layer for sensing. In embodiments described herein, a conductive element overlies and is in communication with an uppermost floating gate conductor. Because the uppermost floating gate conductor may be used to provide array lines (e.g. word lines, bit lines, etc.) and bus lines for accessing/powering the chemical devices, the uppermost floating gate conductor should be a suitable material or mixture of materials and of sufficient thickness therefor. Since the conductive element is within a different layer on the substrate of the chemical device, the conductive element may function as a dedicated sensing surface area independent of the material and thickness of the uppermost floating gate structure. For example, the conductive element may be wider than the uppermost floating gate conductor such that the sensing surface area can be relatively large. For example, the conductive element may be thinner than the uppermost floating gate conductor such that the sensing surface area can provide increased sensitivity for sensing. As a result, low noise chemical devices can be provided in a high density array, such that the characteristics of reactions can be accurately detected.

Additionally, the uppermost floating gate conductor does not need to be pushed to process limits; while adjacent floating gate conductors should have a thickness (i.e. for low resistivity) suitable for carrying high currents, the space between adjacent floating gate conductors does not need to be the minimum space allowed by process design rules. The material(s) used for the uppermost floating gate conductor should be suitable for high currents. Providing the conductive element overlying and in communication with the uppermost floating gate conductor provides greater freedom in choice of material for the conductive element since the conductive element is on a different layer than the uppermost floating gate conductor.

FIG. 1 illustrates a block diagram of components of a system for nucleic acid sequencing according to an exemplary embodiment. The components include a flow cell 101 on an integrated circuit device 100, a reference electrode 108, a plurality of reagents 114 for sequencing, a valve block 116, a wash solution 110, a valve 112, a fluidics controller 118, lines 120/122/126, passages 104/109/111, a waste container 106, an array controller 124, and a user interface 128. The integrated circuit device 100 includes a microwell array 107 overlying a sensor array that includes chemical devices as described herein. The flow cell 101 includes an inlet 102, an outlet 103, and a flow chamber 105 defining a flow path of reagents over the microwell array 107. The reference electrode 108 may be of any suitable type or shape, including a concentric cylinder with a fluid passage or a wire inserted into a lumen of passage 111. The reagents 114 may be driven through the fluid pathways, valves, and flow cell 101 by pumps, gas pressure, or other suitable methods, and may be discarded into the waste container 106 after exiting the outlet 103 of the flow cell 101. The fluidics controller 118 may control driving forces for the reagents 114 and the operation of valve 112 and valve block 116 with suitable software. The microwell array 107 includes an array of reaction regions as described herein, also referred to herein as microwells, which are operationally associated with corresponding chemical devices in the sensor array. For example, each reaction region may be coupled to a chemical device suitable for detecting an analyte or reaction property of interest within that reaction region. The microwell array 107 may be integrated in the integrated circuit device 100, so that the microwell array 107 and the sensor array are part of a single device or chip. The flow cell 101 may have a variety of configurations for controlling the path and flow rate of reagents 114 over the microwell array 107. The array controller 124 provides bias voltages and timing and control signals to the integrated circuit device 100 for reading the chemical devices of the sensor array. The array controller 124 also provides a reference bias voltage to the reference electrode 108 to bias the reagents 114 flowing over the microwell array 107.

During an experiment, the array controller 124 collects and processes output signals from the chemical devices of the sensor array through output ports on the integrated circuit device 100 via bus 127. The array controller 124 may be a computer or other computing means. The array controller 124 may include memory for storage of data and software applications, a processor for accessing data and executing applications, and components that facilitate communication with the various components of the system in FIG. 1. The values of the output signals of the chemical devices indicate physical and/or chemical parameters of one or more reactions taking place in the corresponding reaction regions in the microwell array 107. For example, in an exemplary embodiment, the values of the output signals may be processed using the techniques disclosed in Rearick et al., U.S. patent application Ser. No. 13/339,846, filed Dec. 29, 2011, based on U.S. Prov. Pat. Appl. Nos. 61/428,743, filed Dec. 30, 2010, and 61/429,328, filed Jan. 3, 2011, and in Hubbell, U.S. patent application Ser. No. 13/339,753, filed Dec. 29, 2011, based on U.S. Prov. Pat. Appl. No. 61/428,097, filed Dec. 29, 2010, which are all incorporated by reference herein in their entirety. The user interface 128 may display information about the flow cell 101 and the output signals received from chemical devices in the sensor array on the integrated circuit device 100. The user interface 128 may also display instrument settings and controls, and allow a user to enter or set instrument settings and controls.

In an exemplary embodiment, during the experiment the fluidics controller 118 may control delivery of the individual reagents 114 to the flow cell 101 and integrated circuit device 100 in a predetermined sequence, for predetermined durations, at predetermined flow rates. The array controller 124 can collect and analyze the output signals of the chemical devices indicating chemical reactions occurring in response to the delivery of the reagents 114. During the experiment, the system may also monitor and control the temperature of the integrated circuit device 100, so that reactions take place and measurements are made at a known predetermined temperature. The system may be configured to let a single fluid or reagent contact the reference electrode 108 throughout an entire multi-step reaction during operation. The valve 112 may be shut to prevent any wash solution 110 from flowing into passage 109 as the reagents 114 are flowing. Although the flow of wash solution may be stopped, there may still be uninterrupted fluid and electrical communication between the reference electrode 108, passage 109, and the microwell array 107. The distance between the reference electrode 108 and the junction between passages 109 and 111 may be selected so that little or no amount of the reagents flowing in passage 109 and possibly diffusing into passage 111 reach the reference electrode 108. In an exemplary embodiment, the wash solution 110 may be selected as being in continuous contact with the reference electrode 108, which may be especially useful for multi-step reactions using frequent wash steps.

FIG. 2 illustrates a cross-sectional view of a portion of the integrated circuit device 100 and flow cell 101. During operation, the flow chamber 105 of the flow cell 101 confines a reagent flow 208 of delivered reagents across open ends of the reaction regions in the microwell array 107. The volume, shape, aspect ratio (such as base width-to-well depth ratio), and other dimensional characteristics of the reaction regions may be selected based on the nature of the reaction taking place, as well as the reagents, byproducts, or labeling techniques (if any) that are employed. The chemical devices of the sensor array 205 are responsive to (and generate output signals) chemical reactions within associated reaction regions in the microwell array 107 to detect an analyte or reaction property of interest. The chemical devices of the sensor array 205 may, for example, be chemically sensitive field-effect transistors (chemFETs), such as ion-sensitive field effect transistors (ISFETs). Examples of chemical devices and array configurations that may be used in embodiments are described in U.S. Patent Application Publication No. 2010/0300559, No. 2010/0197507, No. 2010/0301398, No. 2010/0300895, No. 2010/01307a43, and No. 2009/0026082, and U.S. Pat. No. 7,575,865, each of which are incorporated by reference herein in their entirety.

FIG. 3 illustrates a cross-sectional view of two representative chemical devices and their corresponding reaction regions according to an exemplary embodiment. In FIG. 3, two chemical devices 350, 351 are shown, representing a small portion of a sensor array that can include millions of chemical devices. Chemical device 350 is coupled to corresponding reaction region 301, and chemical device 351 is coupled to corresponding reaction region 302. Chemical device 350 is representative of the chemical devices in the sensor array. In the illustrated example, the chemical device 350 is a chemically-sensitive field effect transistor (chemFET), more specifically an ion-sensitive field effect transistor (ISFET) in this example. The chemical device 350 includes a floating gate structure 318 having a sensor plate 320 coupled to the reaction region 301 by a conductive element 307. As is illustrated in FIG. 3, the sensor plate 320 is the uppermost floating gate conductor in the floating gate structure 318. In the illustrated example, the floating gate structure 318 includes multiple patterned layers of conductive material within layers of dielectric material 319. The chemical device 350 also includes a source region 321 and a drain region 322 within a semiconductor substrate 354. The source region 321 and the drain region 322 comprise doped semiconductor material having a conductivity type different from the conductivity type of the substrate 354. For example, the source region 321 and the drain region 322 may comprise doped P-type semiconductor material, and the substrate may comprise doped N-type semiconductor material. Channel region 323 separates the source region 321 and the drain region 322. The floating gate structure 318 overlies the channel region 323, and is separated from the substrate 354 by a gate dielectric 352. The gate dielectric 352 may be silicon dioxide, for example. Alternatively, other dielectrics may be used for the gate dielectric 352.

As shown in FIG. 3, the dielectric material defines the reaction region 301 which may be within opening defined by an absence of dielectric material. The dielectric material 303 may comprise one or more layers of material, such as silicon dioxide or silicon nitride or any other suitable material or mixture of materials. The dimensions of the openings, and their pitch, can vary from implementation to implementation. In some embodiments, the openings can have a characteristic diameter, defined as the square root of 4 times the plan view cross-sectional area (A) divided by Pi (e.g., sqrt(4*A/π), of not greater than 5 micrometers, such as not greater than 3.5 micrometers, not greater than 2.0 micrometers, not greater than 1.6 micrometers, not greater than 1.0 micrometers, not greater than 0.8 micrometers, not greater than 0.6 micrometers, not greater than 0.4 micrometers, not greater than 0.2 micrometers or not greater than 0.1 micrometers.

The chemical device 350 includes a conductive element 307 overlying and in communication with an uppermost floating gate conductor in the plurality of floating gate conductors. The conductive element is wider and thinner than the uppermost floating gate conductor, as illustrated in FIG. 3. In the illustrated embodiment, the dielectric material defines an opening extending to an upper surface of the conductive element. The upper surface 307 a of the conductive element 307 defines a bottom surface of a reaction region for the chemical device. Viewed another way, the upper surface 307 a of the conductive element 307 and a lower portion of an inner surface 1316 a of the dielectric material 1316 define a bottom region of a reaction region for the chemical device. The conductive element 307 may have a width W wider than a width W′ of the reaction region. According to one embodiment, the distance 333 between adjacent conductive elements in the chemical device is about 0.18 microns. According to another embodiment, the thickness 334 of the conductive element is about 0.1-0.2 microns. In one embodiment, the uppermost floating gate conductor in the plurality of floating gate conductors may have a thickness 335 greater than a thickness 335′ of other floating gate conductors in the plurality of floating gate conductors. In another embodiment, the conductive element 370 may comprise a material different from a material comprising the uppermost floating gate conductor.

The upper surface 307 a of the conductive element 307 acts as the sensing surface for the chemical device 350. The conductive element as discussed throughout the disclosure may be formed in various shapes (width, height, etc.) depending on the materials/etch techniques/fabrication processes etc. used during the manufacture process. The conductive element 307 may comprise one or more of a variety of different materials to facilitate sensitivity to particular ions (e.g. hydrogen ions). Accordingly to an exemplary embodiment, the conductive element may comprise at least one of titanium, tantalum, titanium nitrite, and aluminum, and/or oxides and/or mixtures thereof. The conductive element 307 allows the chemical device 350 to have a sufficiently large surface area to avoid the noise issues associated with small sensing surfaces. The plan view area of the chemical device is determined in part by the width (or diameter) of the reaction region 301 and can be made small, allowing for a high density array. In addition, because the reaction region 301 is defined by upper surface 307 a of the conductive element 307 and an inner surface 1316 a of the dielectric material 1316, the sensing surface area depends upon the depth and the circumference of the reaction region 301, and can be relatively large. As a result, low noise chemical devices 350, 351 can be provided in a high density array, such that the characteristics of reactions can be accurately detected.

During manufacturing and/or operation of the device, a thin oxide of the material of the conductive element 307 may be grown on the upper surface 307 a which acts as a sensing material (e.g. an ion-sensitive sensing material) for the chemical device 350. For example, in one embodiment the electrically conductive element may be titanium nitride, and titanium oxide or titanium oxynitride may be grown on the upper surface 307 a during manufacturing and/or during exposure to solutions during use. Whether an oxide is formed depends on the conductive material, the manufacturing processes performed, and the conditions under which the device is operated. In the illustrated example, the conductive element 307 is shown as a single layer of material. More generally, the electrically conductive element may comprise one or more layers of a variety of electrically conductive materials, such as metals or ceramics, or any other suitable conductive material or mixture of materials, depending upon the implementation. The conductive material can be, for example, a metallic material or alloy thereof, or can be a ceramic material, or a combination thereof. An exemplary metallic material includes one of aluminum, copper, nickel, titanium, silver, gold, platinum, hafnium, lanthanum, tantalum, tungsten, iridium, zirconium, palladium, or a combination thereof. An exemplary ceramic material includes one of titanium nitride, titanium aluminum nitride, titanium oxynitride, tantalum nitride, or a combination thereof. In some alternative embodiments, an additional conformal sensing material (not shown) is deposited on the upper surface 307 a of the conductive element 307. The sensing material may comprise one or more of a variety of different materials to facilitate sensitivity to particular ions. For example, silicon nitride or silicon oxynitride, as well as metal oxides such as silicon oxide, aluminum or tantalum oxides, generally provide sensitivity to hydrogen ions, whereas sensing materials comprising polyvinyl chloride containing valinomycin provide sensitivity to potassium ions. Materials sensitive to other ions such as sodium, silver, iron, bromine, iodine, calcium, and nitrate may also be used, depending upon the implementation.

Referring again to FIG. 3, in operation, reactants, wash solutions, and other reagents may move in and out of the reaction region 301 by a diffusion mechanism 340. The chemical device 350 is responsive to (and generates an output signal related to) the amount of a charge 324 proximate to the conductive element 307. The presence of charge 324 in an analyte solution alters the surface potential at the interface between the analyte solution and the upper surface 307 a of the conductive element 307, due to the protonation or deprotonation of surface charge groups caused by the ions present in the analyte solution. Changes in the charge 324 cause changes in the voltage on the floating gate structure 318, which in turn changes in the threshold voltage of the transistor of the chemical device 350. This change in threshold voltage can be measured by measuring the current in the channel region 323 between the source region 321 and a drain region 322. As a result, the chemical device 350 can be used directly to provide a current-based output signal on an array line connected to the source region 321 or drain region 322, or indirectly with additional circuitry to provide a voltage-based output signal.

As described in more detail below with respect to FIGS. 4-14, the conductive element 307 is overlying and in communication with an uppermost floating gate conductor 320. The conductive element is wider and thinner than the uppermost floating gate conductor. Because the charge 324 may be more highly concentrated near the bottom of the reaction region 301, in some embodiments variations in the dimensions of the conductive element may have a significant effect on the amplitude of the signal detected in response to the charge 324. In an embodiment, reactions carried out in the reaction region 301 can be analytical reactions to identify or determine characteristics or properties of an analyte of interest. Such reactions can generate directly or indirectly byproducts that affect the amount of charge adjacent to the conductive element 307. If such byproducts are produced in small amounts or rapidly decay or react with other constituents, multiple copies of the same analyte may be analyzed in the reaction region 301 at the same time in order to increase the output signal generated. In an embodiment, multiple copies of an analyte may be attached to a solid phase support 312, either before or after deposition into the reaction region 301. The solid phase support 312 may be microparticles, nanoparticles, beads, solid or porous comprising gels, or the like. For simplicity and ease of explanation, solid phase support 312 is also referred herein as a particle. The solid phase support may be of varied size, as would be understood by one of ordinary skill in the art. Further, the solid support may be positioned in the opening at various places. For a nucleic acid analyte, multiple, connected copies may be made by rolling circle amplification (RCA), exponential RCA, polymerase chain reaction (PCR) or like techniques, to produce an amplicon without the need of a solid support.

In various exemplary embodiments, the methods, systems, and computer readable media described herein may advantageously be used to process and/or analyze data and signals obtained from electronic or charged-based nucleic acid sequencing. In electronic or charged-based sequencing (such as, pH-based sequencing), a nucleotide incorporation event may be determined by detecting ions (e.g., hydrogen ions) that are generated as natural by-products of polymerase-catalyzed nucleotide extension reactions. This may be used to sequence a sample or template nucleic acid, which may be a fragment of a nucleic acid sequence of interest, for example, and which may be directly or indirectly attached as a clonal population to a solid support, such as a particle, microparticle, bead, etc. The sample or template nucleic acid may be operably associated to a primer and polymerase and may be subjected to repeated cycles or “flows” of deoxynucleoside triphosphate (“dNTP”) addition (which may be referred to herein as “nucleotide flows” from which nucleotide incorporations may result) and washing. The primer may be annealed to the sample or template so that the primer's 3′ end can be extended by a polymerase whenever dNTPs complementary to the next base in the template are added. Then, based on the known sequence of nucleotide flows and on measured output signals of the chemical devices indicative of ion concentration during each nucleotide flow, the identity of the type, sequence and number of nucleotide(s) associated with a sample nucleic acid present in a reaction region coupled to a chemical device can be determined.

FIGS. 4-14 illustrate stages in a manufacturing process for forming an array of chemical devices and corresponding well structures according to an exemplary embodiment. FIG. 4 illustrates a structure 400 including the floating gate structures (e.g. floating gate structure 318) for the chemical devices 350, 351. The structure 400 can be formed by depositing a layer of gate dielectric material on the semiconductor substrate 354, and depositing a layer of polysilicon (or other electrically conductive material) on the layer of gate dielectric material. The layer of polysilicon and the layer gate dielectric material can then be etched using an etch mask to form the gate dielectric elements (e.g. gate dielectric 352) and the lowermost conductive material element of the floating gate structures. Following formation of an ion-implantation mask, ion implantation can then be performed to form the source and drain regions (e.g. source region 321 and a drain region 322) of the chemical devices. A first layer of the dielectric material 319 can be deposited over the lowermost conductive material elements. Conductive plugs can then be formed within vias etched in the first layer of dielectric material 319 to contact the lowermost conductive material elements of the floating gate structures. A layer of conductive material can then be deposited on the first layer of the dielectric material 319 and patterned to form second conductive material elements electrically connected to the conductive plugs. This process can then be repeated multiple times to form the completed floating gate structure 318 shown in FIG. 4. Alternatively, other and/or additional techniques may be performed to form the structure. Forming the structure 400 in FIG. 4 can also include forming additional elements such as array lines (e.g. word lines, bit lines, etc.) for accessing the chemical devices, additional doped regions in the substrate 354, and other circuitry (e.g. access circuitry, bias circuitry etc.) used to operate the chemical devices, depending upon the device and array configuration in which the chemical devices described herein are implemented. In some embodiments, the elements of the structure may, for example, be manufactured using techniques described in U.S. Patent Application Publication No. 2010/0300559, No. 2010/0197507, No. 2010/0301398, No. 2010/0300895, No. 2010/013071a43, and No. 2009/0026082, and U.S. Pat. No. 7,575,865, each of which were incorporated by reference in their entirety above.

As illustrated in the structure 500 illustrated in FIG. 5, a dielectric material 503 may be formed on the sensor plate 320 of the field effect transistor of the chemical device 350. Next, as illustrated in FIG. 6, the dielectric material 503 of the structure 500 in FIG. 5 is etched to form openings 618, 620 (for vias) extending to the upper surfaces of the floating gate structures of the chemical devices 350, 351, resulting in the structure 600 illustrated in FIG. 6. The openings 618, 620 may, for example, be formed by using a lithographic process to pattern a layer of photoresist on the dielectric material 503 to define the locations of the openings 618, 620, and then anisotropically etching the dielectric material 503 using the patterned photoresist as an etch mask. The anisotropic etching of the dielectric material 503 may, for example, be a dry etch process, such as a fluorine based Reactive Ion Etching (RIE) process. In the illustrated embodiment, the openings 618, 620 are separated by a distance 630 and the openings 618, 620 are of a suitable dimension for a via. For example, the separation distance 630 may be a minimum feature size for the process (e.g. a lithographic process) used to form the openings 618, 620. In such a case, the distance 630 may be significantly more than the width 620. Next, a layer of conductive material 704 is deposited on the structure 600 illustrated in FIG. 6, resulting in the structure 700 illustrated in FIG. 7. Conductive material 704 may be referred to as a conductive liner. The conductive material 704 may comprise one or more layers of electrically conductive material. For example, the conductive material 704 may be a layer of titanium nitride, or a layer of titanium. Alternatively, other and/or additional conductive materials may be used, such as those described above with reference to the electrically conductive element. In addition, more than one layer of conductive material may be deposited. The conductive material 704 may be deposited using various techniques, such as sputtering, reactive sputtering, atomic layer deposition (ALD), low pressure chemical vapor deposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD), metal organic chemical vapor deposition (MOCVD), etc.

Next, a layer of conductive material 805 such as tungsten, for example, is deposited on the structure 700 illustrated in FIG. 7, resulting in the structure 800 illustrated in FIG. 8. The conductive material 805 may be deposited using various techniques, such as sputtering, reactive sputtering, atomic layer deposition (ALD), low pressure chemical vapor deposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD), metal organic chemical vapor deposition (MOCVD), etc. or any other suitable techniques. Next, conductive material 704 and conductive material 805 are planarized using a Chemical Mechanical Planarization (CMP) process, for example, resulting in the structure 900 illustrated in FIG. 9. As an optional, additional step, a via barrier liner 1006 may be formed on the planarized conductive material 704 and conductive material 805, resulting in the structure 1000 illustrated in FIG. 10. For example, the via barrier liner 1006 may be titanium nitride. While via barrier liner 1006 is illustrated in the FIGS. 11-14, via barrier liner 1006 is optional.

Next, a conductive material 1107 may be formed on the via barrier liner 1006, resulting in the structure 1100 illustrated in FIG. 11. Optionally, conductive material 1107 may be formed directly on the planarized conductive material 704 and conductive material 805. For example, the conductive material 1107 may be tantalum. Next, the conductive material 1107 is etched to form openings 1208, 1210, 1212 extending to the via barrier liner 1006, resulting in the structure 1200 illustrated in FIG. 12. The openings 1208, 1210, 1212 may, for example, be formed by using a lithographic process to pattern a layer of photoresist on the conductive material 1107 to define the locations of the openings 1208, 1210, 1212, and then anisotropically etching the dielectric material 503 using the patterned photoresist as an etch mask. The anisotropic etching of the conductive material 1107 may, for example, be a dry etch process, such as a fluorine based Reactive Ion Etching (RIE) process. In the illustrated embodiment, the openings 1208, 1210, 1212 are separated by a distance 1230L. Conductive element 1107 has a height 1230H. Length 1230L of conductive element 1107 is greater than length 320L of sensor plate 320. The thickness 1230H of conductive element 1107 is less than the thickness 320H of sensor plate 320. The spaces (i.e. 1220) between conductive material elements in conductive material 1107 are smaller than the spaces (i.e. 1220′) between sensor plates. The conductive element need not be directly above and/or aligned with the uppermost floating gate conductor.

Next, a dielectric material 1316 may be formed on the structure 1200 illustrated in FIG. 12, resulting in the structure 1300 illustrated in FIG. 13. For example, the dielectric material 1316 may be tetraethyl orthosilicate, (TEOS) or silicon dioxide. Next, the dielectric material 1316 of the structure 1300 in FIG. 13 is etched to form openings 1418, 1420 extending to the upper surfaces of the floating gate structures of the chemical devices 350, 351, resulting in the structure 1400 illustrated in FIG. 14.

FIG. 15 illustrates a block diagram of an exemplary chemical device including an exemplary sensor region and an exemplary peripheral region, according to an embodiment. The chemical device 1500 may include a sensor region 1501 containing the chemically-sensitive field effect transistor and a peripheral region 1503 containing peripheral circuitry to obtain a signal from the chemically-sensitive field effect transistor. In one embodiment, the conductive element is within a conductive layer that is only within the sensor region 1501. In another embodiment, the conductive element comprises a material not within the peripheral region 1503. The sensor region and peripheral region illustrated in FIG. 15 are not meant to be limiting as to shape or size or location, for example, on the chemical device.

While the present invention is disclosed by reference to the preferred embodiments and examples detailed above, it is to be understood that these examples are intended in an illustrative rather than in a limiting sense. It is contemplated that modifications and combinations will readily occur to those skilled in the art, which modifications and combinations will be within the spirit of the invention and the scope of the following claims. 

1. A chemical device, comprising: a chemically-sensitive field effect transistor including a floating gate structure comprising a plurality of floating gate conductors electrically coupled to one another; a conductive element overlying and in communication with an uppermost floating gate conductor in the plurality of floating gate conductors, the conductive element wider and thinner than the uppermost floating gate conductor; and a dielectric material defining an opening extending to an upper surface of the conductive element.
 2. The chemical device of claim 1, wherein the conductive element comprises at least one of titanium, tantalum, titanium nitrite, and aluminum, and/or oxides and/or mixtures thereof.
 3. The chemical device of claim 1, wherein the distance between adjacent conductive elements in the chemical device is about 0.18 microns.
 4. The chemical device of claim 1, wherein the thickness of the conductive element is about 0.1-0.2 microns.
 5. The chemical device of claim 1, wherein the uppermost floating gate conductor in the plurality of floating gate conductors has a thickness greater than a thickness of other floating gate conductors in the plurality of floating gate conductors.
 6. The chemical device of claim 1, wherein the conductive element comprises a material different from a material comprising the uppermost floating gate conductor.
 7. The chemical device of claim 1, wherein an inner surface of the dielectric material and the upper surface of the conductive element define an outer surface of a reaction region for the chemical device.
 8. The chemical device of claim 1, wherein the plurality of floating gate conductors is within a layer that includes array lines and bus lines.
 9. The chemical device of claim 1, including a sensor region containing the chemically-sensitive field effect transistor and a peripheral region containing peripheral circuitry to obtain a signal from the chemically-sensitive field effect transistor.
 10. The chemical device of claim 9, wherein the conductive element is within a conductive layer that is only within the sensor region.
 11. The chemical device of claim 9, wherein the conductive element comprises a material not within the peripheral region.
 12. The chemical device of claim 1, wherein the chemically-sensitive field effect transistor includes a floating gate structure comprising a plurality of conductors electrically coupled to one another and separated by dielectric layers, and the floating gate conductor is an uppermost conductor in the plurality of conductors.
 13. The chemical device of claim 1, wherein a first layer of the dielectric material is silicon nitride and a second layer is at least one of silicon dioxide and tetraethyl orthosilicate, and the second layer defines sidewalls of the opening.
 14. The chemical device of claim 1, further comprising: a microfluidic structure in fluid flow communication with the chemically-sensitive field effect transistor, and arranged to deliver analytes for sequencing.
 15. A method for manufacturing a chemical device, the method comprising: forming a chemically-sensitive field effect transistor including a floating gate structure comprising a plurality of floating gate conductors electrically coupled to one another; forming a conductive element overlying and in communication with an uppermost floating gate conductor in the plurality of floating gate conductors, the conductive element wider and thinner than the uppermost floating gate conductor; and forming a dielectric material defining an opening extending to an upper surface of the conductive element.
 16. The method for manufacturing a chemical device of claim 15, wherein the upper surface of the conductive element defines a bottom surface of a reaction region for the chemical device.
 17. The method for manufacturing a chemical device of claim 15, wherein an inner surface of the dielectric material and the upper surface of the conductive element define an outer boundary of a reaction region for the chemical device.
 18. The method for manufacturing a chemical device of claim 15, wherein the conductive element is formed within a conductive layer that is only within a sensor region of the chemical device. 